1. Field of the Invention
The invention relates to a method for the preparation of metal-free strips in the metal vapor deposition of an insulating tape which is intended for use in electric capacitors, in which the insulating tape is covered in the region of the metal-free strips to be prepared, by an endless cover tape which rests against the insulating tape and travels along with the same velocity as the former. The cover tape is coated with oil on the side facing the metal evaporator before entering the vapor deposition zone. After traversing the vapor deposition zone and, after the cover tape and the insulating tape go their different ways, the cover tape is freed of vapor-deposited metal by stripping it off.
The invention further relates to apparatus for carrying out the method, which contains a cooling cylinder; a metal evaporator which is arranged, in the travel direction of the covering tape, ahead of the metal evaporator; supply rolls of the tapes to be metallized, and a cleaning device which is arranged in the travel direction ahead of the oil evaporator.
2. Description of the Prior Art
A method for preparing metal-free strips in the metal vapor deposition of tape is shown in U.S. Pat. No. 2,898,241. This method attempts to achieve a delineation as sharp as possible of the metal layer applied to the insulating tape. By using mask-like apertures above the metal evaporator, which are arranged at a larger distance from the insulating tape, the edges of the metal strip produced decrease toward the surface of the insulating tape. If this gradual transition is to be replaced by a sharp delineation of the metal strip, an endless cover tape which may if desired, be covered with wax, grease or oil, is used such that this tape runs past the metal evaporator in direct contact with the insulating tape and at the same velocity. After this cover tape is removed, the sharp edge desired there is produced. The covering of the metal-free strips carried out in this manner results in the oil film covering only the cover tape and does not extend slightly to the surface of the insulating tape. In particular, in the case of metal films which must be called thick in this connection (corresponding to a conductivity of up to 15 S), sharp edges are a disadvantage because they lead to breakdowns of the counterelectrode in the region of the edges; this applies particularly if the capacitors of such metallized insulating tapes are intended for a-c voltage and application for high voltages.
In German Published Prosecuted Application DE-AS No. 26 52 438, a method for preparing metal-free strips in the metal vapor deposition of an insulating tape are described. The method corresponds to what is described in U.S. Pat. No. 2,898,241. The same comments therefore apply to both cases.
From German Pat. No. 12 62 732 is furthermore known a method to prepare on an insulating tape strips free of metal by vapor-depositing covering means such as oil or grease on the parts of the tape to be left free. Vapor-deposition substances mentioned as suitable are diffelene, apiezone oil and silicone oils.
Both methods are not very suitable for preparing free margins for use in vapor-depositing relatively thick metal films, since an oil coverage cannot prevent metal precipitation in vapor-depositing thick layers, while a tape coverage of the type mentioned does not provide satisfactory results. If an additional coverage adjacent to the carrier is used, sharp edges, burrs and breaks even occur at the coatings, which can lead to damage to the capacitor to be wound.